Mechanical wave transmission device



March 15, 1932 E, K. SANDEMAN 1,849,641 I MECHANICAL WAVE TRANSMISSION DEVICE Filed May 16, 1930 ZSheets-Sheet l //Vl/E/V7'0H E h. SANDEMAN A r TURNEY March 15, 1932. E. K. SANDEMAN MECHANICAL WAVE TRANSMISSION DEVICE Filed May 16, 1930 2 Sheets-Sheet //Vl/E/V7'0/? E. K SANDEMAM A T TOHNEY Patented Mar. 15, 1932 EDWARD KENNETH SANDEFIAN, OF ALDWYCH, LONDON, ENGLAND, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, 015 NEW YORK, N. Y., A CORPORA- TION OF NEW YORK MECHANICAL WAVE TRANSMISSION DEVICE Application filed May 16, 1930, Serial No. 452,912, and in France September 30, 1929.

This invention relates to wave transmission and more particularly to mechanical means for selectively altering the character of wave motion.

An object of the invention is to improve the quality of transmitted signals;

Another object is to shift the phase relations of mechanical waves over a range of frequency;

Another object is to obtain a mechanical vibratory network equivalent to a given electrical network;

A further object is to obtain a mechanical lattice, or bridged, structure equivalent to an electrical lattice network.

It has been recognized that corresponding quantities in mechanical and electrical systems are:

-11! echam'cal system Electrical system Force Displacement Velocity Mass 'Stifiness Friction The theory and design formulae developed for electrical networks are made equally applicable to mechanical networks by replacing each electrical quantity with the corresponding quantity of the mechanical system.

Up to the present time there are known only a limited number of types of mechanical as structures in which these electrical-mechanical conversions can be made. In accordance with this invention there are provided new mechanical structures comprising a plurality of interconnected arms bearing masses and elastances which act as mechanical impedance elements. The component arms are con nected together in the desired configuration by means of lever arrangements to which the arms are pivoted, so that free relative m0- tion among the various arms is permitted.

A feature of the invention is a lattice arrangement of the arms bearing the impedance elements.

Another feature is means for tensioning the mechanical structure to secure intimate contact between the moving parts and to obtain freedom from backlash.

The invention will be more clearly understood from the following detailed description and the accompanying drawings, of which,

Figs. 1 and 2 illustrate electrical lattice networks;

Fig. 3 illustrates a mechanical network embodying the invention, equivalent tothe electrical network of Fig. 1;

Fig. 4 shows another embodiment of the invention equivalent to the electrical network of Fig. 2;

Fig. 5 shows a perspective View of the structure of Fig. 3; and

Fig. 6 illustrates another embodiment of the invention, equivalent to the electrical network of Fig. 1.

Fig. 1 illustrates schematically a balanced electrical net work section included in a line terminated by a resistance. The section comprises equal series condensers of capacity C farads and equal bridging inductances of in ductance L henrys. Fig. 2 illustrates a line comprising an electrical lattice section having equal anti-resonant series arms and equal resonant bridge arms.

It is well known that electrical networks of the lattice type shown in Figs. 1 and 2 have substantially no attenuation, but an appreciable phase shift, over the range of frequencies to be transmitted, provided the relation holds at all frequencies of that range.

impedance terminating the section. Such networks may be used to produce a delay which varies with frequency or which is substantially independent of frequency for use in echo suppressors, voice operated repeaters or other purposes. A more complete discussion of the impedance and propagation constant of lattice networks is given in U. S. Patent 1,608,305. The propagation constant, P, is in general a complex quantity of the form P=A +jB (2) ture is assembled in a frame, or casing, 1,

upon which the moving parts are mounted. The structure is composed of similar recurrent sections, one section of which is described as follows: Lozenge-shaped levers 2 of rigid material having negligible weight are freely pivoted at their centers upon pivots 3 mounted-upon the base. The extremities of levers 2 are freely pivoted upon pivots 5 to the ends of light rigid rods 4, the ppo site ends of which are pivoted upon pivots 7 to the centers ,of lozenge-shaped levers 6.

T'heouter extremities of levers 6 are connect- I ed by light rigid rods, or bars, 8, pivoted at the ends by pivots 14. The bars 8, which have negligible mass, are'connected to the frame by springs 9, which tend to impede motion of the bars in the direction parallel to their length. The inner extremities of levers 6 are diagonally interconnected b rigid bars 18 carrying masses 10, the bars being freely pivoted to the levers by pivots 15.

Any number of these sections may be joined in tandem, as indicated by the partially shown sections joined at either end at pivots of levers 2.

The input terminals of the section are points 5 on line Y and the output terminals are points 5 on line Z, or vice versa. The terminals, however, could as well be points 7 on levers 6; that is to say, levers 2 are not essential to the operation of the system, but serve primarily to fasten the structure to the base at pivots 3. In a system of several sections it is necessary that only the ends of the system be held in place by such members as levers 2. Thus, the levers 2 may be considered as associated with the sending and receiving end impedance; they may be said to form part of the sending and receiving mechanism.

Motion is transmitted from each end of the sending mechanism to the receiving mechanism through a pair of parallel paths, namely rods 8 and 18, which connect to opposite sides of the receiving mechanism. By virtue of this opposing connection of the parallel paths of each pair of rods, motion of one of the pair produces motion of the receiving mechanism in the opposite direction to which the same motion of the other of the pair' would produce. This is a fundamental characteristic of lattice networks, both electrical and mechanical.

It should be noted here that the system would operate if there were employed a single pair of parallel impedance paths, instead of the two pairs. Thus, if lower point 5 in line Y, lower points 14 and upper right point L W and where M is the mass in grams of each mass element 10 together with the associated rod 18, and S is the stiffness in dynes per centimeter of each of the springs 9.

These relations assume that the masses and elastances of the rods and levers and the friction at the pivots are negligible. The reason the impedance elements of the mechanical system are equivalent to only onequarter, instead of the full value, of the corresponding electrical'impedances is that the levers act as mechanical transformers, which for the case at hand, where the center pivots are midway between the end pivots, exert an impedance transformation ratio of 1 to 4. This transformation is more fully explained in an article on pages 800 to 819 of Philosophical Magazine October, 1927, entitled A theory of the torque converter by E. K. Sandeman.

Under the conditions of Equations 8 and 4c, the characteristic impedance R in dynes per centimeter per second, of the mechanical structure, numerically equals K.

The equivalence between the structures of Figures 1 and 3 may be explained as follows:

The four terminals of the mechanical network corresponding to the four terminals of the electrical network, are the four points 5, these being efiectively the same as the four points 7. In the case of the electrical network, a current entering any of the four terminals divides and flows partly through an inductance and partly through a capacity. In the case of the mechanical network, a displacement of any of the four terminals is distributed between the stiffness 9 and the mass 10, in the inverse order of their impedances, by means of the lever 6. The remainder of the equivalence depends upon the proper substitution of grams for henrys, centimeters per dyne for farads, and dynes per centimeter per second for ohms. This proper substitution in any particular case involves the application of a numerical force factor to obtain the mechanical elements. For example, where it is desired to insert a mechanical network between two electrical-mechanical translating devices, the force factor is the ratio of the force in dynes to the current producing this force. The mechanical inertances and stifinesses are obtained by multiplying the corresponding electrical quantities by this factor.

Fig. 4: illustrates a mechanical network which is the mechanical analogue of the electrical lattice of Fig. 2. The constitution of the system and its equivalence to the corresponding electrical network follow from the description and discussion of Fig. 3.

Fig. 5 illustrates one form of physical embodiment of the structure of Fig. 3. The same reference numbers are used in both figures to designate members fulfilling like functions. Spring supports 11 are fastened to the casing (not shown) by screws passing through holes 12 and engaging in slots in the casing parallel to the main axis of motion XX. Similarly, the bearings, or pivots, 3 are mounted on supports (not shown) also secured to the casing by screws engaging in slots running parallel to ads XX. These spring and bearing supports are the only points of attachment to the casing. The springs 9 are fiat pieces of elastic material of small weight, one end of each spring being suitably fastened to the spring support and the other end to the associated bar 8. The masses 10 are prisms of a relatively heavy material provided with extensions at each end which constitute the arms, or rods, 18 which attach to levers 6 at pivot points 15. The rods 4 and 8 are in the form of channel beams, this construction furnishing a bar which is light and rigid. The levers 2 and 6 are constructed of any suitable light rigid material. All the pivot junctions of levers and rods, namely, junction points 5, 7, 14 and 15 are constituted by cementing or otherwise suitably fastening a flap or extension of one of the connecting members to the other. A suitable flap may be an integral part of one of the connecting members, such as the extension at 14 of bar 8, shaved down to the condition of a metallic foil which freely bends without appreciable friction.

In order to take up any initial sl-ackness and insure that every member is in intimate contact with its associated member, the supports of the end bearings 2 of a number of such sections, connected together, are strained away from one another either by means of springs connected between the end bearing supports and the casing, or by arranging the axis vertically and hanging a weight from the bottom bearing. Such a strain is applied with all the screws securing the bearing supports and the supports 11 loosened; the screws are then tightened with the strain still on, after which, if desired, the strain may be released.

Fig. 6 shows another embodiment of the invention equivalent to the electrical lattice of Fig. 1, parts fulfilling the same functions as corresponding parts in Figs. 3 and 5 being designated by the same numbers. In this figure all the essential parts are shown except the frame, or casing, to which the levers 2 must be pivoted at pivots 3 and to which the outer ends of springs 9 must be secured. The principal difference between the structures of Figs. 5 and 6 is that the arms 4: are cords or wires which are kept in tension by fastening the pivots 3 and the springs 9 to the base so that this condition of tension is obtained. It was explained in the discussion of Fig. 5 how this tensioning may be effected.

In utilizing any of the embodiments of the invention in a mechanical wave transmission line, pivot points 5, or alternatively points 7, of the initial section are connected to the source of vibration, such as for example, the two extremities of a balanced armature of a telephone receiver. The receivingend is like wise connected to the receiving device which must also be adapted to be pivoted at points 5 or 7, of the receiving end section. The transmission of the mechanical vibrations through the network will be modified in accordance with its wave transmission characteristic.

It is understood that the invention is not limited to the specific embodiments herein described, but only in accordance with the scope of the appended claims.

What is claimed is:

1. A mechanical vibratory lattice network comprising bars in series with the line of motion and bars bridging the line of motion, said bars being interconnected by pivoted levers, said series bars being constrained by springs and said bridging bars by masses.

2. A base and a mechanical vibratory lattice network, according to claim 1, in which points on said levers midway between the points at which said bars are pivoted, are pivoted to members which in turn are pivoted to the extremities of levers Whose midpoints are pivoted to said base and the extremities of said springs are fastened to said base.

3. In a mechanical Wave transmission system, in combination, a sending end mechanism, a receiving end mechanism, a pair of impedance bearing members for transmitting vibrations in parallel between one end of said 10 A sending mechanism and said receiving mechanism, lever arrangements for connecting said members to said mechanisms, and motion reversing means for causing motion of one of said members to move said receiving mechas nism in the opposite direction in which motion of the other of said members causes the receiving mechanism to move.

4. The combination of claim 3 in which said motion reversing means is a lever pivoted to a 2 1 lXBCl; base, said parallel vibration transmitting members being freely pivoted to points on said reversing lever onopposite sides of said fixed pivot. I

In Witness whereof, I hereunto subscribe 5- my name this fifteenth day of April, 1930.

EDVVARD KENNETH SANDEMAN. 

